Linking multiple databases to posts

Dear WordPress-gurus,

I am working on a new website which I am building with a three other mates. The website will create an overview of exclusive cars and exclusive car dealers. Most of the dealers we cooperate with use software that controls their inventory. With that software it is possible to easily copy the data from their software to other websites (their own website or a website such as the one we are building). This means that they don’t have to give in all the data on each separate website but only have to do it once in their software, saving a lot of time and effort. The data of the cars is then send via a XML feed and is interpreted by a plugin which is installed on our website. This plugin reads the XML files, import the into a database and creates a new WordPress post linked to the car (in a separate post-type where all the car posts are visible).

The aspect that causes problems is as follows: this is a different database than the one where the WordPress posts are saved, however in the database where the cars are located is the WordPress-ID available.

Sometimes the data that is send and imported via the XML feed isn’t fully complete or has to be changed. This can be done via the database, however the chance of doing something wrong in the database resulting in a website crash is a bit too big in my opinion (two mates doesn’t know how to deal with databases).

The question is: is it possible to link two databases (the one where the car data is stored in and the one where the WordPress posts are stored in) in order to make it possible for us to change data or fill in extra data in the backend of WordPress? And if this is possible, how can this be done?

Many many thanks in advance and I hope someone can and is willing to help us out. I’ve already searched google and WordPress for it but I couldn’t find the right way to make it work for our website. So if you have tips or knows a right tutorial, you will be a true hero!

Kind regards,
Jordy